Catheter with irrigated tip electrode with porous substrate and high density surface micro-electrodes

ABSTRACT

A catheter has a multifunctional “virtual” tip electrode with a porous substrate and a multitude of surface microelectrodes. The surface microelectrodes are in close proximity to each other and in a variety of configurations so as to sense tissue for highly localized intracardiac signal detection, and high density local electrograms and mapping. The porous substrate allows for flow of conductive fluid for ablating tissue. The surface microelectrodes can be formed via a metallization process that allows for any shape or size and close proximity, and the fluid “weeping” from the porous substrate provides more uniform irrigation in the form of a thin layer of saline. The delivery of RF power to the catheter tip is based on the principle of “virtual electrode,” where the conductive saline flowing through the porous tip acts as the electrical connection between the tip electrode and the heart surface. The substrate and the surface electrodes are constructed of MRI compatible materials so that the physician can conduct lesion assessment in real time during an ablation procedure. The surface electrodes include noble metals, including, for example, platinum, gold and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of and claims priority to and thebenefit of U.S. application Ser. No. 16/551,300 filed Aug. 26, 2019, nowU.S. Pat. No. 10,925,668, which is a continuation of and claims priorityto and the benefit of U.S. patent application Ser. No. 16/049,737 filedJul. 30, 2018, now U.S. Pat. No. 10,390,880, which claims priority toand the benefit of U.S. application Ser. No. 14/586,907, filed Dec. 30,2014, now U.S. Pat. No. 10,034,707, the entire contents of all of whichare incorporated herein by reference.

FIELD OF INVENTION

This invention relates to catheters and electrophysiologic catheters, inparticular, catheters for cardiac tissue ablation and diagnostics.

BACKGROUND

Cardiac arrhythmia, such as atrial fibrillation, occurs when regions ofcardiac tissue abnormally conduct electric signals to adjacent tissue,thereby disrupting the normal cardiac cycle and causing asynchronousrhythm. Important sources of undesired signals are located in varioustissue regions in or near the heart, for example, the ventricles, theatria and/or and adjacent structures such as areas of the pulmonaryveins. Regardless of the sources, unwanted signals are conductedabnormally through heart tissue where they can initiate and/or maintainarrhythmia.

Procedures for treating arrhythmia include surgically disrupting theorigin of the signals causing the arrhythmia, as well as disrupting theconducting pathways for such signals. More recently, it has been foundthat by mapping the electrical properties of the heart muscle inconjunction with the heart anatomy, and selectively ablating cardiactissue by application of energy, it is possible to cease or modify thepropagation of unwanted electrical signals from one portion of the heartto another. The ablation process destroys the unwanted electricalpathways by formation of non-conducting lesions.

In this two-step procedure—mapping followed by ablation—electricalactivity at points in the heart is typically sensed and measured byadvancing a catheter containing one or more electrical sensors into theheart, and acquiring data at a multiplicity of points. These data arethen utilized to select the target areas at which ablation is to beperformed.

A typical ablation procedure involves the insertion of a catheter havinga tip electrode at its distal end into a heart chamber. A referenceelectrode is provided, generally taped to the patient's skin. Radiofrequency (RF) current is applied to the tip electrode, and flowsthrough the surrounding media, i.e., blood and tissue, toward thereference electrode. The distribution of current depends on the amountof electrode surface in contact with the tissue, as compared to bloodwhich has a higher conductivity than the tissue. Heating of the tissueoccurs due to its electrical resistivity. If the tissue is heatedsufficiently, cellular and other protein destruction ensues; this inturn forms a lesion within the heart muscle which is electricallynon-conductive. During this process, heating of the electrode alsooccurs as a result of conduction from the heated tissue to the electrodeitself. If the electrode temperature becomes sufficiently high, possiblyabove 50 degree C., blood clot could form on the surface of theelectrode. If the temperature continues to rise, more blood clot isformed while dehydration ensues.

The tip temperature increase and the associated clot formation have twoconsequences: increased electrical impedance and increased probabilityfor stroke. The former relates to clot dehydration. Because dehydratedbiological material has a higher electrical resistance than hearttissue, impedance to the flow of electrical energy into the tissue alsoincreases. Increased impedance leads to sub-optimal energy delivery tothe tissue which results in inadequate lesion formation, reducedablation efficiency and eventually to sub-optimal clinical outcome. Thelatter, a safety hazard, is due to possible dislodgment of the formedclot and relocation in the brain vasculature. It is therefore beneficialfrom a safety perspective as well as ablation efficiency to minimize thetip temperature increase and clot formation. This should be accomplishedwithout compromising the formation of lesions of appropriate sizes.

In a typical application of RF current to the endocardium, circulatingblood provides some cooling of the ablation electrode. However, there istypically a stagnant area between the electrode and tissue which issusceptible to the formation of dehydrated proteins and coagulum. Aspower and/or ablation time increases, the likelihood of an impedancerise also increases. As a result of this process, there has been anatural upper bound on the amount of energy which can be delivered tocardiac tissue and therefore the size of RF lesions. In clinicalpractice, it is desirable to reduce or eliminate impedance rises and,for certain cardiac arrhythmias, to create larger lesions. One methodfor accomplishing this is to monitor the temperature of the ablationelectrode and to control the RF current delivered to the ablationelectrode based on this temperature. If the temperature rises above apre-selected value, the current is reduced until the temperature dropsbelow this value. This method has reduced the number of impedance risesduring cardiac ablations but has not significantly increased lesiondimensions. The results are not significantly different because thismethod continues to rely on the cooling effect of the blood which isdependent on the location within the heart and the orientation of thecatheter to the endocardial surface.

Another method is to irrigate the ablation electrode, e.g., withphysiologic saline at room temperature, to actively cool the ablationelectrode instead of relying on the more passive physiological coolingprovided by the blood. Additionally, due to the irrigation-mediateddilution of blood around the tip, the probability for clot creation isfurther reduced. Thus, irrigation tip cooling and blood dilution allowfor safer increase of applied RF power. This results in lesions whichtend to be larger usually measuring about 10 to 12 mm in depth.

The clinical effectiveness of irrigating the ablation electrode isdependent upon the distribution of flow within and around the surface ofthe tip electrode structure as well as the rate of irrigation flowthrough the tip. Effectiveness is achieved by reducing the overallelectrode temperature and eliminating hot spots in the ablationelectrode which can initiate coagulum formation. More channels andhigher flows are more effective in reducing overall temperature andtemperature variations, i.e., hot spots. Irrigation is utilized duringthe entire time the catheter resides inside the patient's body. Higherflow rate is used during ablation while lower-maintenance-flow rate isrequired in order to prevent back flow of blood into the coolantpassages during non-ablation time. The coolant flow rate must bebalanced against the amount of fluid that can be safely injected intothe patient. Thus, reducing coolant flow by utilizing it as efficientlyas possible is a desirable design objective.

One method for designing an ablation electrode which efficientlyutilizes coolant flow is the use of a porous material structure. Suchdesigns have the advantage of distributing the coolant evenly across theentire electrode structure. This balanced cooling results in a)eradication of possible surface or interior hot spots, and b) uniformdilution of blood at the vicinity of the electrode, thus furtherminimizing the chance for clot formation. Such designs are described inU.S. Pat. Nos. 6,405,078 and 6,466,818 to Moaddeb et al., the entiredisclosures of which are incorporated herein by reference. Moaddebdescribes the use of sintered metal particles to create a porous tipelectrode. In addition, Moaddeb uses a non-conductive insert implantedinto the porous tip electrode for mounting a thermocouple, lead wireand/or irrigation tube within the porous tip electrode. However, duringirrigation the sintered metal particles can disintegrate and break awayfrom the electrode structure. This-undesirable-particle dislodgement maybe further facilitated during ablation. Additionally, (and in thecontext of our MRI compatibility claims—see below) the metallic materialproposed for such porous tip is not optimal for MRI imaging.Furthermore, the proposed tip does not allow for high density mapping—ahighly desired feature for accurate arrhythmia diagnosis. Consequently,a desire arises for a porous electrode having increased structuralintegrity, being compatible with the MRI environment, and allowing forhigh mapping density.

A porous tip electrode catheter is also described in U.S. Pat. No.8,262,653 to Plaza. The porous tip electrode comprises a porous materialthrough which fluid can pass. The porous tip electrode is covered with athin coating of conductive metal having openings (pores) through whichfluids can pass. However, the porosity of such thin conductive coatingis not easily controlled leading to inconsistent pore size anddistribution. Therefore, distribution of irrigation fluid around the tipelectrode may not be even or uniform. Furthermore, in this design, RFpower delivery is achieved via direct connection (e.g. by soldering orother similar technique) of the RF power line to the tip's outerconductive coat. Thus, the presence of the generally non-uniform porouscoating is necessary in order to establish electrical contact of the tipto the heart tissue.

Safe and efficacious ablation depends not only on optimal irrigationarrangement for the tip but also on accurate mapping of theelectrophysiological behavior of the heart, which would allow foraccurate diagnosis and appropriate tissue targeting. The greater theaccuracy of the mapping the more accurate the diagnosis and thus theeffectiveness of treatment. Improved (high resolution) cardiac mappingrequires the use of a multitude of electrodes in close proximity tosense electrical activity within a small area, for example, a squarecentimeter or less.

Metallization of ceramics is a well-established technique and is widelyused in a multitude of electronics and engineering disciplines,including fabrication of RF electronic circuits. Metallization involvesthe application of metal on ceramic substrates, including the formationof conductive regions, such as metallized conductor patterns or uniformmetal layers on surfaces of ceramic substrates. Common ceramicsubstrates include aluminum oxide, beryllium oxide, ferrite, bariumtitanate, as well as quartz or borosilicate. Generally, ceramicmetallization processes fall into three categories: thin-film,thick-film, and co-firing techniques. In the thin film approach, a thinlayer of metal is deposited by vacuum processes such as sputtering,evaporation, chemical vapor deposition, and laser ablation. Electrolessand electrolytic plating are also frequently grouped in the thin filmcategory. To enhance adhesion, a preliminary adhesion-promoting layer,such as chromium or titanium, is often deposited. Thick film methodsinvolve printing metal pastes, typically metal powders mixed with glassfrits and organic binders onto ceramic substrates. The printedsubstrates are fired to form conductive paths on the ceramic. In theco-firing approach, unfired “green” ceramic surfaces are coated withpatterned metal paste lines. The printed green ceramic is fired both tosinter the material and form the conductive metal patterns.Metallization processes are described, for example, in U.S. Pat. No.4,547,094 to DeLuca, et al.; U.S. Pat. No. 5,096,749 to Harada, et al.;U.S. Pat. No. 5,690,805 to Thorn, et al.; and U.S. Pat. No. 5,725,938Jin, et al. Metallization depending on the type of metallization processand the substrate may include gold, platinum, or other biocompatiblemetals suitable for intracardial signal acquisitions.

While ablation has revolutionized the treatment of cardiac arrhythmias,ablation can be improved where physicians can assess lesions in realtime. The use of magnetic resonance imaging (MRI) during an ablationprocedure could enable physicians to assess lesions in real time.However, the ablation catheter and other associated accessory equipmentcan interfere with the imaging process, causing local distortions in theMRI scans. Use of appropriate MRI compatible materials is necessary tominimize these image distortions. Safety experts have cleared somemetals for use during MRIs, including titanium, cobalt-chromium, copper,selected stainless steel alloys. Non-ferromagnetic metals are also MRIcompatible. Such materials include copper, brass, silver, gold,aluminum, lead, magnesium, platinum and tungsten. Ceramic materials aswell as other thermoplastic polymers are non-metallic and as such arehighly desirable as MRI compatible materials. They not only presentminimal image distortion but being electrical insulators they present noheating effects due to absence of internally induced electricalcurrents. Ceramic materials of porous construction are proposed in thecurrent invention as materials for the construction of the catheter'stip.

In view of the foregoing, it is desirable to provide a catheter with adome tip electrode made of a porous substrate for more uniformirrigation, where the dome tip electrode incorporates surface electrodesmade via a metallization, printing or other process for any desirablesurface electrode pattern that provides multiple electrodes in closeproximity for high density mapping. It is also desirable to provide acatheter where the substrate and the surface electrodes are MRIcompatible so that the physician can conduct lesion assessment in realtime during an ablation procedure.

SUMMARY OF THE INVENTION

The present invention is directed to a catheter having a multifunctional“virtual” tip electrode with a porous substrate and a multitude ofsurface microelectrodes. The surface microelectrodes in close proximityto each other and in a variety of configurations sense tissue for highlylocalized intracardiac signal detection, and high density localelectrograms and mapping and the porous substrate allows for flow ofconductive fluid for ablating tissue. The surface microelectrodes can beformed via a metallization process that allows for any shape or size andclose proximity, and the fluid “weeping” from the porous substrateprovides more uniform irrigation in the form of a thin layer of saline.The delivery of RF power to the catheter tip is based on the principleof “virtual electrode,” where the conductive saline flowing through theporous tip acts as the electrical connection between the tip electrodeand the heart surface.

Moreover, the substrate and the surface electrodes are constructed ofMRI compatible materials so that the physician can conduct lesionassessment in real time during an ablation procedure. The surfaceelectrodes include noble metals, including, for example, platinum, goldand combinations thereof.

In some embodiments, the catheter includes an elongated catheter body,and a distal electrode member having a porous substrate and a pluralityof distinct surface microelectrodes. A plurality of lead wires areconnected to the surface microelectrodes for transmitting electricalsignals sensed by the microelectrodes. The porous substrate has aninterior chamber adapted to receive conductive fluid which is inelectrical contact with a lead wire that extends into the chamber,wherein such electrified fluid passes from the chamber to outside thesubstrate for distal irrigation and tissue ablation.

In some detailed embodiments, the porous substrate is comprised of aceramic material. The substrate has a plurality of surfacemicroelectrodes ranging between about one and 20. Each surfacemicroelectrode has a surface area ranging between 0.2 mm² and 2 mm².

In some detailed embodiments, the porous substrate and the chamber bothhave a generally cylindrical shape, with a generally uniform wallthickness between the chamber and the outer surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of a catheter of the present invention, inaccordance with one embodiment.

FIG. 2A is a side cross-sectional view of the catheter of FIG. 1,including a junction between a catheter body and a deflection section,taken along a first diameter.

FIG. 2B is a side cross-sectional view of the catheter of FIG. 1,including the junction of FIG. 2A, taken along a second diametergenerally perpendicular to the first diameter.

FIG. 2C is an end cross-sectional view of the deflection section ofFIGS. 2A and 2B, taken along line C-C.

FIG. 3A is a side cross-sectional view of the catheter of FIG. 1,including a junction between the deflection section and a distalelectrode section, taken along a first diameter.

FIG. 3B is a side cross-sectional view of the junction of FIG. 3A, takenalong a second diameter generally perpendicular to the first diameter.

FIG. 4 is a side cross-sectional view of the catheter of FIG. 1,including a distal electrode section.

FIG. 4A is an end cross-sectional view of the distal electrode sectionof FIG. 4, taken along line A-A.

FIG. 4B is an end cross-sectional view of the distal electrode sectionof FIG. 4, taken along line B-B.

FIG. 4C is a side view of a distal portion of a lead wire in a chamber,in accordance with one embodiment.

FIG. 4D is a side view of a distal portion of a lead wire in a chamber,in accordance with another embodiment.

FIG. 4E is a side view of a distal portion of a lead wire in a chamber,in accordance with another embodiment.

FIG. 4F is a side view of a distal portion of a lead wire in a chamber,in accordance with another embodiment.

FIG. 4G is a side view of a distal portion of a lead wire and anirrigation tubing in a chamber, in accordance with another embodiment.

FIG. 5A is a side view of a tip electrode in accordance with a firstembodiment.

FIG. 5B is a side view of a tip electrode in accordance with a secondembodiment.

FIG. 5C is a side view of a tip electrode in accordance with a thirdembodiment.

FIG. 5D is a side view of a tip electrode in accordance with a fourthembodiment.

FIG. 5E is a side view of a tip electrode in accordance with a fifthembodiment.

FIG. 6 is a side cross-sectional view of a porous substrate, inaccordance with another embodiment.

FIG. 7 is a side cross-sectional view of a porous substrate, inaccordance with yet another embodiment.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the invention, there is provided a steerablecatheter having an irrigated tip adapted for diagnostic and/ortherapeutic procedures. As shown in FIG. 1, catheter 10 comprises anelongated catheter body 12 having proximal and distal ends, anintermediate deflection section 14 extending from a distal end of thecatheter body 12, a tip electrode section 15 extending from a distal endof the catheter body 12, and a control handle 16 at the proximal end ofthe catheter body 12.

With reference to FIGS. 2A and 2B, the catheter body 12 comprises anelongated tubular construction having a single, axial or central lumen18. The catheter body 12 is flexible, i.e., bendable but substantiallynon-compressible along its length. The catheter body 12 can be of anysuitable construction and made of any suitable material. In oneembodiment, the catheter body 12 comprises an outer wall 22 made of apolyurethane or PEBAX. The outer wall 22 comprises an imbedded braidedmesh of high-strength steel, stainless steel or the like to increasetorsional stiffness of the catheter body 12 so that, when the controlhandle 16 is rotated axially, the rest of the catheter, including thesections 14 and 16, also rotates axially. The outer diameter of thecatheter body 12 is not critical, but is preferably no more than about 8french, more preferably about 7 french, still more preferably about 5french. Likewise, the thickness of the outer wall 22 is not critical,but is thin enough so that the central lumen 18 can accommodate anirrigation tube, puller wire(s), lead wires, and any other wires, cablesor tubes. The inner surface of the outer wall 22 is lined with astiffening tube 20, which can be made of any suitable material, such aspolyimide or nylon. The stiffening tube 20, along with the braided outerwall 22, provides improved torsional and longitudinal stability. Theouter diameter of the stiffening tube 20 is about the same as orslightly smaller than the inner diameter of the outer wall 22. Polyimidetubing is presently preferred for the stiffening tube 20 because it maybe very thin walled while still providing very good stiffness. Thismaximizes the diameter of the central lumen 18 without sacrificingstrength and stiffness. A particularly preferred catheter has an outerwall 22 with an outer diameter of from about 0.090 inches to about 0.098inches and an inner diameter of from about 0.061 inches to about 0.065inches and a polyimide stiffening tube 20 having an outer diameter offrom about 0.060 inches to about 0.064 inches and an inner diameter offrom about 0.051 inches to about 0.056 inches.

As shown in FIGS. 2A, 2B, and 2C, the intermediate deflectable section14 comprises a short section of tubing 19 having multiple lumens,including off-axis lumens 30, 32, 34 and 35. The tubing 19 is made of asuitable non-toxic material that is preferably more flexible than thecatheter body 12. In one embodiment, the material for the tubing 19 isbraided polyurethane, i.e., polyurethane with an imbedded mesh ofbraided high-strength steel, stainless steel or the like. The outerdiameter of the deflection section 14, like that of the catheter body12, is preferably no greater than about 8 french, more preferably about7 french, still more preferably about 5 french. The size of the lumensis not critical. In one embodiment, the deflection section 14 has anouter diameter of about 7 french (0.092 inches) and the second lumen 32and third lumen 34 are generally about the same size, each having adiameter of from about 0.020 inches to about 0.024 inches, preferablyabout 0.022 inches, with the first and fourth lumens 30 and 35 having aslightly larger diameter of from about 0.032 inches to about 0.038inches, preferably about 0.036 inches.

A means for attaching the catheter body 12 to the deflection section 14is illustrated in FIGS. 2A and 2B. The proximal end of the deflectionsection 14 comprises an outer circumferential notch 24 that receives theinner surface of the outer wall 22 of the catheter body 12. Thedeflection section 14 and catheter body 12 are attached by adhesive(e.g. polyurethane glue) or the like. Before the deflection section 14and catheter body 12 are attached, however, the stiffening tube 20 isinserted into the catheter body 12. The distal end of the stiffeningtube 20 is fixedly attached near the distal end of the catheter body 12by forming a glue joint (not shown) with polyurethane glue or the like.Preferably, a small distance, e.g., about 3 mm, is provided between thedistal end of the catheter body 12 and the distal end of the stiffeningtube 20 to permit room for the catheter body 12 to receive the notch 24of the deflection section 14. A force is applied to the proximal end ofthe stiffening tube 20, and, while the stiffening tube 20 is undercompression, a first glue joint (not shown) is made between thestiffening tube 20 and the outer wall 22 by a fast drying glue, e.g.Super Glue®. Thereafter, a second glue joint (not shown) is formedbetween the proximal ends of the stiffening tube 20 and outer wall 22using a slower drying but stronger glue, e.g. polyurethane.

At the distal end of the deflection section 14 is the distal tipelectrode section 15 having a connector tube 27 and a tip electrode 36.In the illustrated embodiment of FIGS. 3A and 3B, the connector tube 27is a relative short piece of tubing, about 1 cm in length, for example,made of polyetheretherketone (PEEK). The proximal end of the connectortube 27 has a circumferential notch whose outer surface is surrounded byan inner surface of a circumferential notch formed in the distal end ofthe tubing 10 of the deflection section 14. The ends are bonded to eachother by polyurethane glue or the like.

As shown in FIG. 4, the tip electrode 36 has a diameter about the sameas the outer diameter of the tubing 19 and the connector tube 27. Thetip electrode 36 includes a porous substrate 38 and a plurality ofsurface electrodes 40. The porous substrate 38 is formed by porousceramic material or any other suitable non-conductive polymer, such aspolyethylene, or polytetrafluoroethylene (e.g., Teflon®). In theillustrated embodiment, the substrate 38 has an elongated cylindricalshape with a narrower proximal stem portion 38N. The substrate 38 isformed with an interior chamber 37 that also has a similar elongatedcylindrical shape extending longitudinally in the substrate 38. In oneembodiment, the porous substrate 38 has a total length ranging fromabout 6 mm to about 9 mm, more preferably about 7 mm. For a 7 mm longtip electrode, each of the body form 38B and the proximal stem portion38N may have a length of about 3.5 mm.

The chamber 37 has an opening 37P at the proximal end of the substrate38 and a distal end 37D near the distal end of the substrate. It isunderstood that the chamber 37 and the substrate need not have the samegeneral shape, and further that depending on the volume of the chamber37 the thickness T of the wall between the chamber 37 and the outersurface of the substrate may be varied as desired or appropriate.

Abutting the proximal face of the substrate stem portion 38N, a plugmember 41 seals the proximal face and plugs the opening thus enclosingthe chamber 37. As shown in FIG. 4, the plug member 41 has a firstthrough-hole 51 for lead wire 48 to pass through and enter into thechamber 37 and a second through-hole 52 for receiving a distal end of anirrigation tubing 50 which supplies fluid, e.g., saline or anyelectrically conductive fluid, into the chamber 37.

In the embodiment of FIG. 4, the proximal stem portion 38N is receivedin a distal end of the connector tube 27. The stem portion 38N and theconnector tube 27 are attached by polyurethane glue or the like.

The porous non-conductive material of the substrate 38 can be made usingany conventional technique In the illustrated embodiment, thenon-conductive material comprises sintered ceramic powder, or polymerparticles formed from polyethylene or Teflon. As used herein, the term“sinter” refers to the process of bonding adjacent particles in a powdermass or compacting the particles by heating them to a temperature belowthe melting point of the main constituent at a predetermined and closelycontrolled time-temperature regime, including heating and coolingphases, in a protective atmosphere. The porosity of the sinteredmaterial is controlled by the amount of particle compacting in the moldor glue, the particle size, and the particle distribution. The sinteredparticles permit passage of a cooling fluid through the tip electrode,as described in more detail below. The final shape of the tip can beobtained with a variety of techniques including machining, grinding,etching, or molding.

In one embodiment, a sintering process involves providing ceramic,polyethylene or Teflon powder particles in a certain sieve fraction,e.g., in the range of from about 5 microns to about 250 microns. Theparticles are preferably in the range of from about 10 microns to about100 microns. In a particularly preferred embodiment, at least twodifferent sized particles can be provided. For example, particles in therange of from about 15 microns to about 30 microns, and more preferablyabout 20 microns, in combination with particles in the range of fromabout 80 microns to about 110 microns, and more preferably about 100microns, could be used. When two different sized particles are used,preferably the larger particles have a mean diameter at least about 2.5times greater than the mean diameter of the smaller particles, and morepreferably at least about 4 times greater. Alternatively, a singleparticle size can be used, which can provide a denser packing and resultin a higher pressure drop across the porous electrode. Whatever materialis used, the particles are preferably rounded and more preferablyspherical, so as to provide a tip electrode surface that is not rough.However, the particles can be irregularly shaped, i.e. having differingshapes, which is a low cost alternative. Tip surface irregularitiescould also be smoothed through secondary operations such as mechanicalpolishing and laser etching.

In one process, the particles are put into a mold, such as a ceramicmold, having the desired electrode shape. If desired, the particles canbe mixed with a suitable binder prior to being put into the mold. When abinder is used, the mold containing the binder and particles is placedinto a low temperature oven and heated to a temperature sufficient toevaporate the binder. The particles are then sintered under vacuum orair at a temperature ranging from about 80 degree C. to about 160 degreeC., although the temperature can vary depending on the composition ofthe porous polymer. However, the temperature should be below the meltingpoint of the composition. The resulting tip electrode is then removedfrom the mold and assembled onto the flexible tubing of the tip section.

In the embodiment of FIG. 4, the porous substrate 38 has a generallycylindrical shape with domed distal end. However, it is understood thatthe porous substrate may have different shapes, as desired orappropriate. For example, porous substrate 138 of FIG. 6 has a bulbousshape and an elongated stem portion 138N, along with a bulbous shapedchamber 137 with an elongated proximal portion 137P. The wall thicknessT is generally uniform throughout the substrate 138. Moreover, it isunderstood that the porous substrate and the chamber may have dissimilarshapes. For example, substrate 238 of FIG. 7 is generally cylindricalwith a domed distal end, but its chamber 237 is cylindrical with anarrowed distal end 237D which is adapted for receiving and anchoring adistal end of the electrifying lead wire. Likewise, the wall thicknessmay vary throughout the substrate, some portions T1 being thinner andother portions T2 being thicker.

Disposed over the surface of the porous substrate are the one or moresensing microelectrodes 40 in the form of individual and separate thinmetal coatings, as depicted in FIGS. 5A-5D. It is understood that thethin metal coatings may be applied in close proximity to each otherusing any suitable process, including, for example, metallization, coreplating, electroplating and/or 3-D printing, and may involve more thanone layers, with the outer most layer comprising suitable electrodematerial (or alloys) known in the art, such as gold, platinum,platinum/iridium. In accordance with a feature of the present invention,the one or more metal coatings are made of conductive material that isalso MRI-compatible, (e.g. platinum or gold). In some embodiments, themetal coating 40 is made of a platinum-iridium alloy, e.g. 90%Platinum/10% Iridium, applied to the surface of the porous substrate 38by metallization treatment or process impregnating a thin layer ofplatinum-iridium alloy onto the porous substrate 38, as known in theart.

The thickness of the metal coating may vary as desired. The thicknesscan be uniform or not uniform. For example, the metal coating may have auniform thickness ranging from 0.2 μm to about 2.0 μm. In someembodiments, coating forming one or more microelectrodes 40X, as shownin FIGS. 5A and 5B, has non-uniform thickness e.g. thicker towards thecenter and thinner towards the periphery. This allows for a protrusionconfiguration or a raised profile. The ratio of the central thickness Hto the thickness at the periphery may range between about 2 and 20.Such-protruding-shape allows for improved contact with the heart tissueand consequently improved electrogram quality.

As shown in FIGS. 5A-5E, the metal coatings can be of any desiredplurality and of any desired configuration and/or orientation to formindividual and separate surface micro-electrodes, for example, circular,oval, rectangular, elongated, ring, axial, radial, and co-centric. Forexample, in FIG. 5A, the metal coatings provide axial proximalrectangular surface micro-electrodes 40T, more distal ring surfacemicro-electrodes 40R, and distal tip circular surface micro-electrode40C. For example, in FIG. 5B, the metal coatings provide axial proximalrectangular surface micro-electrodes 40TP and axial distal rectangularsurface micro-electrodes 40TD that are axially offset from each other.For example, in FIG. 5C, the metal coatings provide a plurality (four)of rings surface micro-electrodes 40R and a distal tip circular surfacemicro-electrode 40C. For example, in FIG. 5D, the metal coatings providea distal tip circular surface micro-electrode 40C, a plurality ofsmaller circular micro-electrodes 40C and a proximal ring surfacemicro-electrode 40R. For example, in FIG. 5E, a series of concentriccircular surface micro-electrodes 40C1, 40C2 and 40C3 of different radiiis shown on one side of the tip. It is understood that the size of themicro-surface electrodes in the drawings herein, including FIGS. 5A-5E,is not to scale and that their size is exaggerated so as to show theirstructure with better clarity.

Advantageously, the surface electrodes 40 are sized as micro-electrodesfor obtaining highly localized electrograms and providing high densitymapping of heart tissue. The surface area of each surface electroderanges between about 0.2 mm² and 2.0 mm², preferably between about 0.5mm² and 1 mm². In that regard, it is understood that the figures hereinare not necessarily to scale. The plurality of surface electrodes on thesubstrate may range between about one and 20, preferably about two and10. Each surface electrode 40 is connected to a respective lead wire 46whose proximal end terminates in the control handle 16 in an input jack(not shown) that may be plugged into an appropriate signal processor(not shown). The lead wires 46 extend from the control handle 16 andthrough the central lumen 18 of the catheter body (FIG. 2A), the firstlumen 30 of tubing 19 of the deflection section 14 (FIG. 2A), and thelumen of the connector tube 27 (FIG. 3A). The portion of the lead wires46 extending through at least the catheter body 12 and the deflectionsection 14 may be enclosed within a protective sheath (not shown), whichcan be made of any suitable material, preferably polyimide. Theprotective sheath may be anchored at its distal end to the proximal endof the deflection section 14 by gluing it in the first lumen 30 withpolyurethane glue or the like.

The lead wires 46 are attached or electrically connected to the surfaceelectrodes 40 through surface electrode leads 60 (FIGS. 5A-5E) which maybe applied or deposited on the outer surface of the porous substrate 38and the stem portion 38N in the same manner as the surfacemicroelectrodes 40, as described above. As shown in FIGS. 4 and 4B,distal end portions of lead wires 46 pass between an inner surface ofthe connector tubing 27 and the peripheral edge of the plug member 41and the outer surface of the stem portion 38N. These surfaces at andnear the proximal end of the substrate 38 may be sealed by glue and thelike. Distal ends of the lead wires 46 are attached to respectiveproximal ends of the surface electrode leads 60 at or near the distalend of the connector tubing 27. Accordingly, electrical signals of theheart tissue sensed by the microelectrodes are transmitted proximallytoward the control handle via the surface electrode leads 60 and thelead wires 46.

As understood by one of ordinary skill in the art, selected surfaceelectrode leads 60 and surface sensing microelectrodes 40 are insulatedfrom each other where they overlap each other. An insulating layer maybe placed in between surface electrode leads 60 and surface electrodes40 and grooves 92 (FIGS. 5A, 5C and 5E) may be formed on the outersurface of the porous substrate for underpassing surface electrode leads60 so that overlying surface electrodes 40 can lie flat on the outersurface of the porous substrate 38.

For ablation purposes, the porous substrate 38 is “energized” by thelead wire 48 which passes into the chamber 37 via the first through-hole51 in the plug member 41. When energized, the lead wire 48 renders theporous substrate 38 into a “virtual” ablation electrode by conductingthe energy through the conductive-irrigation fluid, e.g., saline,delivered by the irrigation tubing 50 which enters the chamber 37 andweeps through the porous substrate 38 in providing a generally uniformthin layer of energized fluid throughout its exposed surfaces 62 (inbetween the surface microelectrodes 40) to further improve ablationsafety. Wherever the fluid is present on or flowing from the poroussubstrate 38, ablation may be accomplished therefrom.

In the embodiment of FIG. 4, the distal portion of the lead wire 48 inthe chamber 37 is elongated and linear. However, it is understood thatthe distal portion may assume any shape as desired or appropriate. Thedistal portion of the lead wire 48 in the chamber 37 may be configurednonlinearly, for example, wrapped around itself (FIG. 4D) or coiledaround a support member 53 (FIG. 4C) for increased surface area exposureand contact with the fluid in the chamber 37 for greater conductionbetween the lead wire and the fluid. A proximal end of the supportmember 53 may be affixed to and mounted on a distal face of the plugmember.

The distal portion of the lead wire 48 may also extend linearly anddeeply distally in the chamber 37 along the longitudinal center axis(FIG. 4E), spiral widely approaching the inner surface of the chamber 37(FIG. 4F), or be wrapped or coiled around an extended distal portion ofthe irrigation tubing 40 such that both extend deeply distally in thechamber 37. The irrigation tubing 40 may be perforated with pores 54along its length (FIG. 4G). Such configuration improves the uniformityof irrigation within the chamber 37 and the tip 36 and allows for evengreater exposure of the lead wire to the conductive fluid.

In the illustrated embodiment, the catheter includes three ringelectrodes 39 proximal of the distal tip section 15, mounted on thetubing 19 of the deflection section 14 and/or the connector tubing 27,as shown in FIGS. 3A, 3B and 4. It is understood that the presence andnumber of ring electrodes 39 may vary as desired, likewise theirfunction as monopolar or bipolar electrodes for local electrogramsensing and/or location referencing in relation to the location sensor64 housed in the connector tubing 27. Each ring electrode 39 is slidover the tubing 19 and/or 27 and fixed in place by glue or the like. Thering electrodes 39 can be made of any suitable material, and arepreferably machined from platinum-iridium bar (90% platinum/10%iridium), gold, or gold alloys.

Connection of a lead wire 49 to a ring electrode 39 is preferablyaccomplished by first making a small hole through the tubing 19 and/or27. Such a hole can be created, for example, by inserting a needlethrough the tubing and heating the needle sufficiently to form apermanent hole. A lead wire 49 is then drawn through the hole by using amicrohook or the like. The ends of the lead wire 49 are then stripped ofany coating and soldered or welded to the underside of the ringelectrode 39, which is then slid into position over the hole and fixedin place with polyurethane glue or the like.

The irrigation tubing 50 is provided within the catheter body 12 forinfusing fluids, e.g. saline, to electrify the porous substrate 38 ofthe tip electrode 36 and provide cooling during ablation. The irrigationtubing 50 may be made of any suitable material, and is preferably madeof polyimide tubing. In one embodiment, the irrigation tubing has anouter diameter of from about 0.032 inches to about 0.036 inches and aninner diameter of from about 0.027 inches to about 0.032 inches.

The irrigation tubing 50 extends from the control handle 16 and throughthe central lumen 18 of the catheter body 12 (FIG. 2A), the lumen 35 ofthe tubing 19 of the deflection section 14 (FIG. 3A), and the connectortube 27 (FIG. 3A), and into the second through-hole 52 in the plugmember 41 and the chamber 37 of the substrate 38 (FIG. 4). The proximalend of the irrigation tubing 50 extends through the control handle 16 toa fluid source and a pump (not shown). The fluid introduced through thecatheter is preferably a biologically compatible fluid such as saline,or water. In addition to, or instead of, being used to cool the tipelectrode, the infused fluid also forms a buffer layer to maintainbiological materials, such as blood, at a distance from the tipelectrode, thereby minimizing contact of the tip electrode with thebiological material. This buffer layer reduces coagulation of biologicalmaterials and regulates the impedance or resistance to energy transferof the tissue near the tip electrode during ablation. Saline or anyother conductive fluid is preferred where the tip electrode is tofunction as an ablative electrode.

The rate of fluid flow through the catheter may be controlled by anysuitable fluid infusion pump or by pressure. A suitable infusion pump isthe COOLFLOW available from Biosense Webster, Inc. (Diamond Bar,Calif.). The rate of fluid flow through the catheter preferably rangesfrom about 0.5 ml/min to about 30 ml/min, more preferably from about 2ml/min to about 17 ml/min. Preferably, the fluid is maintained at aboutroom temperature.

It is understood that a temperature sensing means is provided for thetip electrode 36, as known in the art. Any conventional temperaturesensing means, e.g., a thermocouple or thermistor, may be used. Asuitable thermistor for use in the present invention is Model No.AB6N2-GC14KA143E/37C sold by Thermometrics (New Jersey). The temperaturesensing means may also be used as a feedback system to adjust the RFpower delivered to the tissue through the catheter to maintain a desiredtemperature at the tip electrode.

As shown in FIGS. 2B and 3B, a pair of puller wires 70 and 72 extendthrough the catheter body 12 for bidirectional deflection. The pullerwires 70 and 72 are anchored at their proximal end to the control handle16, and are anchored at their distal ends to the deflection section 14at or near its the distal end. The puller wires are made of any suitablemetal, such as stainless steel or Nitinol, and may be coated with Teflonor the like. The coating imparts lubricity to the puller wires. Each ofthe puller wires may have a diameter ranging from about 0.006 inches toabout 0.010 inches.

A compression coil 74 is situated within the catheter body 12 insurrounding relation to each puller wire 50 (FIG. 2B). Each compressioncoil 74 extends from the proximal end of the catheter body 12 to aboutthe proximal end of the deflection section 14. The compression coils aremade of any suitable metal, preferably stainless steel. Each compressioncoil 52 is tightly wound on itself to provide flexibility, i.e.,bending, but to resist compression. The inner diameter of thecompression coil is slightly larger than the diameter of the pullerwire. The Teflon coating on the puller wires 70 and 72 allows them toslide freely within their respective compression coil. If desired,particularly if the lead wires 48 and 49 are not enclosed by aprotective sheath, the outer surface of each compression coil can becovered by a flexible, non-conductive sheath 76, e.g., made of polyimidetubing, to prevent contact between the compression coil and any otherwires within the catheter body 12.

Each compression coil 74 is anchored at its proximal end to the proximalend of the stiffening tube 20 in the catheter body 12 by a glue joint(not shown) and at its distal end to the deflection section 14 by gluejoint 73 (FIG. 2B). Both glue joints may comprise polyurethane glue orthe like. The glue may be applied by means of a needle or the likethrough a hole made in the side wall of the respective tubing, whichneedle is heated sufficiently to form a permanent hole. The glue is thenintroduced through the hole and wicks around the outer circumference toform a glue joint about the entire circumference of the compressioncoil.

The puller wires 70 and 72 extend into the lumens 32 and 34 (FIG. 2C),respectively, of the deflection section 14. The puller wires areanchored at their distal end to the deflection section 14. In oneembodiment, an anchor is fixedly attached to the distal end of eachpuller wire, as depicted in FIG. 3B. The anchor is preferably formed bya metal tube 77, e.g. a short segment of hypodermic stock, which isfixedly attached, e.g. by crimping, to the distal end of the pullerwires 70 and 72. The tubes 77 have a section that extends a shortdistance beyond the distal end of the puller wires. A cross-piece 83made of a small section of stainless steel ribbon or the like issoldered or welded in a transverse arrangement to the distal end of eachtube section 77, which is flattened during the operation. This creates aT-bar anchor. Two notches are created in the sidewall of the deflectionsection 14, resulting in openings into the lumens 32 and 34 into whichthe puller wires 70 and 72 extend. The anchors lie partially within thenotches. Because the length of the ribbons forming the cross-pieces 83are longer than the diameter of the openings into the lumens 32 and 34,the anchors cannot be pulled completely into the lumens 32 and 34. Thenotches are then sealed with polyurethane glue or the like to give asmooth outer surface. Within the lumens 32 and 34 of the deflectionsection 14, each of the puller wires 70 and 72 extends through arespective plastic, preferably Teflon sheath 86, which prevents thepuller wires from cutting into the wall of the tubing 19 when thedeflection section 14 is deflected.

Longitudinal movement of the puller wires 70 and 72 relative to thecatheter body 12, which results in deflection of the deflection section14, is accomplished by suitable manipulation of the control handle 16. Asuitable control handle for use with the present invention is describedin U.S. Pat. No. 6,120,476, the disclosure of which is incorporatedherein by reference.

In the illustrated embodiment, an electromagnetic sensor 64 is providedand housed in the lumen of the connector tube 27. A sensor cable 90extends from the control handle 16, and through the central lumen 18 ofthe catheter body 12 and the lumen 30 of the tubing 19 of deflectionsection 14 and the lumen of the connector tube 27. The sensor cable 90extends out the proximal end of the control handle 16 within anumbilical cord (not shown) to a sensor control module (not shown) thathouses a circuit board (not shown). Alternatively, the circuit board canbe housed within the control handle 16, for example, as described inU.S. Pat. No. 5,964,757, the disclosure of which is incorporated hereinby reference. The electromagnetic sensor cable 90 comprises multiplewires encased within a plastic covered sheath. In the sensor controlmodule, the wires of the electromagnetic sensor cable are connected tothe circuit board. The circuit board amplifies the signal received fromthe electromagnetic sensor and transmits it to a computer in a formunderstandable by the computer by means of the sensor connector at theproximal end of the sensor control module. Also, because the catheter isdesigned for single use only, the circuit board preferably contains anEPROM chip which shuts down the circuit board approximately 24 hoursafter the catheter has been used. This prevents the catheter, or atleast the electromagnetic sensor, from being used twice. Suitableelectromagnetic sensors for use with the present invention aredescribed, for example, in U.S. Pat. Nos. 5,558,091, 5,443,489,5,546,951, 5,568,809 and 5,391,199 and International Publication No. WO95/02995, the disclosures of which are incorporated herein by reference.A preferred electromagnetic sensor 64 has a length of from about 6 mm toabout 7 mm and a diameter of about 1.3 mm.

In use, a suitable guiding sheath (not shown) is inserted into thepatient with its distal end positioned at or near a desired tissuelocation for diagnostics such as mapping and/or treatment such asablation. An example of a suitable guiding sheath for use in connectionwith the present invention is the Preface Braided Guiding Sheath,commercially available from Biosense Webster, Inc. (Diamond Bar,Calif.). The catheter 10 is passed through the guiding sheath andadvanced therethrough to the desired tissue location. The guiding sheathis pulled proximally, exposing the tip electrode section 15 and thedeflection section 14.

The user actuates a thumb knob on the control handle to deflect thecatheter and position the tip electrode 36 on tissue surface. With themultiple surface microelectrodes 40 in contact (or close proximity) withtissue, the catheter 10 is adapted for high density electrode sensingdetecting electrical activity in the tissue which is transmitted throughthe catheter via the lead wires 46 for processing by a signal processor(not shown) for generating high density mapping with highly localizedelectrograms. If ablation is desired, the lead wire 48 is energized byan energy source, e.g., RF generator (not shown), whose distal endportion in the chamber 37 of the porous substrate 38 electrifies theconductive irrigation fluid delivered into the chamber 37 via irrigationtubing 50. Passing of such electrified fluid from the chamber to theexposed surfaces of the porous substrate 38 renders the porous substrate38 into a “virtual” ablation electrode. During and after ablation, thesurface microelectrodes 40 on the porous substrate 38 can senseelectrical activity at and around the ablated tissue to confirm theformation of electrically blocked tissue regions.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. As understood by one of ordinary skill in the art, thedrawings are not necessarily to scale. Also, different features of moreor more embodiment may be combined as needed or appropriate. Moreover,the catheters described herein may be configured to apply various energyforms, including microwave, laser, RF and/or cryogens. Accordingly, theforegoing description should not be read as pertaining only to theprecise structures described and illustrated in the accompanyingdrawings, but rather should be read consistent with and as support tothe following claims which are to have their fullest and fair scope.

What is claimed is:
 1. A catheter comprising: an elongated catheterbody; a distal electrode member comprising: a porous substrate having aninterior chamber adapted to receive conductive fluid, a plurality ofdistal surface ring electrodes arranged on an outer surface of theporous substrate, and a plurality of proximal surface electrodesarranged on the porous substrate proximal of the plurality of distalsurface electrodes, the plurality of proximal surface electrodes beingspaced apart from each other along a circumference of the poroussubstrate; a plurality of proximal lead traces, each of the plurality ofproximal lead traces being connected to a respective one of theplurality of proximal surface electrodes; a plurality of distal leadtraces, each of the plurality of distal lead traces being connected to arespective one of the plurality of distal surface ring electrodes, atleast one of the plurality of distal lead traces having a portionextending underneath at least one other of the plurality of distalsurface ring electrodes; and a chamber lead wire having a distal portionextending into the interior chamber, the chamber lead wire adapted toelectrify the conductive fluid in the interior chamber; the poroussubstrate being configured to pass the conductive fluid from theinterior chamber to the outer surface of the porous substrate.
 2. Thecatheter of claim 1, further comprising at least one insulating layerbetween the at least one other of the plurality of distal surface ringelectrodes and the portion of the at least one of the plurality ofdistal lead traces extending underneath the at least one other of theplurality of distal surface ring electrodes.
 3. The catheter of claim 1,wherein the porous substrate comprises an MRI-compatible material. 4.The catheter of claim 1, wherein the surface electrodes comprise anMRI-compatible material.
 5. The catheter of claim 1, further comprising:a distal tip surface electrode at a distal tip of the distal electrodemember and distal of the plurality of distal surface ring electrodes;and a distal tip electrode lead trace connected to the distal tipsurface electrode, the distal tip electrode lead trace having a portionextending underneath each of the plurality of distal surface ringelectrodes.
 6. A catheter comprising: an elongated catheter body; adistal electrode member comprising: a porous substrate having aninterior chamber adapted to receive conductive fluid, a plurality ofdistal surface electrodes arranged on an outer surface of the poroussubstrate, and one or more proximal surface ring electrodes arranged onthe porous substrate proximal of the plurality of distal surfaceelectrodes; one or more proximal lead traces, each connected to arespective one of the one or more proximal surface ring electrodes; aplurality of distal lead traces, each of the plurality of distal leadtraces being connected to a respective one of the plurality of distalsurface electrodes, each of the plurality of distal lead traces having aportion extending underneath each of the one or more proximal surfacering electrodes; and a chamber lead wire having a distal portionextending into the interior chamber, the chamber lead wire adapted toelectrify the conductive fluid in the interior chamber; the poroussubstrate being configured to pass the conductive fluid from theinterior chamber to the outer surface of the porous substrate.
 7. Thecatheter of claim 6, further comprising at least one insulating layerbetween the one or more proximal surface ring electrodes and the portionof the each of the plurality of distal lead traces extending underneaththe one or more proximal surface ring electrodes.
 8. The catheter ofclaim 6, wherein the porous substrate comprises an MRI-compatiblematerial.
 9. The catheter of claim 6, wherein the surface electrodescomprise an MRI-compatible material.
 10. The catheter of claim 6,further comprising: a distal tip surface electrode at a distal tip ofthe distal electrode member and distal of the plurality of distalsurface electrodes; and a distal tip electrode lead trace connected tothe distal tip surface electrode, the distal tip electrode lead tracehaving a portion extending underneath each of the one or more proximalsurface ring electrodes.
 11. The catheter of claim 6, wherein theplurality of distal surface electrodes comprises a plurality of firstdistal surface electrodes arranged generally along a first circumferenceof the porous substrate, and a plurality of second distal surfaceelectrodes arranged generally along a second circumference of the poroussubstrate, the first circumference being proximal of the secondcircumference, and the plurality of first distal surface electrodesbeing axially offset from the plurality of second distal surfaceelectrodes.
 12. The catheter of claim 11, wherein the plurality ofdistal lead traces comprises: a plurality of first distal lead traces,each of the plurality of first distal lead traces being connected to arespective one of the plurality of first distal surface electrodes; anda plurality of second distal lead traces, each of the plurality ofsecond distal lead traces being connected to a respective one of theplurality of second distal surface electrodes, at least one of theplurality of second distal lead traces having a portion extendingbetween two adjacent ones of the plurality of first distal surfaceelectrodes.
 13. The catheter of claim 11, further comprising: a distaltip surface electrode at a distal tip of the distal electrode member anddistal of the plurality of second distal surface electrodes; and adistal tip electrode lead trace connected to the distal tip surfaceelectrode, the distal tip electrode lead trace having a first portionextending underneath each of the one or more proximal surface ringelectrodes, a second portion extending underneath at least one of theplurality of first distal surface electrodes, and a third portionextending between at least two adjacent ones of the plurality of seconddistal surface electrodes.
 14. A catheter comprising: an elongatedcatheter body; a distal electrode member comprising: a porous substratehaving an interior chamber adapted to receive conductive fluid, and aplurality of concentric circular surface electrodes arranged on an outersurface of the porous substrate, each of the concentric circular surfaceelectrodes having a different radius; a plurality of electrode leadtraces, each of the plurality of electrode lead traces being connectedto a respective one of the plurality of concentric circular surfaceelectrodes; and a lead wire having a distal portion extending into theinterior chamber, the lead wire configured to electrify the conductivefluid in the chamber; the porous substrate being configured to pass theconductive fluid from the chamber to the outer surface of the poroussubstrate.
 15. The catheter of claim 14, wherein the porous substratecomprises an MRI-compatible material.
 16. The catheter of claim 14,wherein the surface electrodes comprise an MRI-compatible material. 17.The catheter of claim 14, further comprising: a distal tip surfaceelectrode at a distal tip of the distal electrode member and distal ofthe plurality of concentric circular surface electrodes; and a distaltip electrode lead trace connected to the distal tip surface electrode.18. The catheter of claim 14, wherein: the plurality of concentriccircular surface electrodes comprises at least one outer circularelectrode having a first radius, and at least one inner circularelectrode having a second radius, the first radius of the outer circularelectrode being greater than the second radius of the inner circularelectrode; and the plurality of electrode lead traces comprises an outerlead trace connected to the outer circular electrode, and an inner leadtrace connected to the inner circular electrode, the inner lead tracehaving a portion extending underneath a portion of the outer circularsurface electrode.
 19. The catheter of claim 14, wherein the pluralityof concentric circular surface electrodes comprises an outer circularsurface electrode having a first radius, an inner circular surfaceelectrode having a second radius smaller than the first radius, and oneor more intermediate circular surface electrodes between the innercircular surface electrode and the outer circular surface electrode, aradius of each of the one or more intermediate circular surfaceelectrodes being smaller than the first radius of the outer circularsurface electrode and greater than the second radius of the innercircular surface electrode.
 20. The catheter of claim 19, wherein theradius of each successive one of the one or more intermediate surfaceelectrodes increases from the inner circular surface electrode towardthe outer circular surface electrode.